PROJECT SUMMARY Fusarium molds are ubiquitous in the environment, where they are major causes of agricultural disease worldwide. Clinically, Fusarium species are incidental and accidental causes of human disease. However, Fusarium molds are the most common cause of fungal keratitis (and microbial keratitis in general) in developing countries and the leading cause of blindness among fungal keratitis patients. In industrialized countries, an outbreak of fusarium keratitis was reported in 2005 and 2006 in regions of the United States not usually associated with fungal keratitis. The outbreak was also reported in Britain, France, Hong Kong, and Singapore. This proposal will focus on fusarium keratitis using the complementary strengths in comparative genomics in PI Ma?s lab, and a murine model of fusarium keratitis developed at our collaborator Dr. Pearlman?s lab. Comparative genomics studies focused on plant pathogenic F. oxysporum isolates demonstrated for the first time that horizontal transfer of supernumerary (SP) chromosomes conveys plant host-specific pathogenicity. A recent study of a F. oxysporum clinical isolate revealed four unique SP chromosomes and confirmed that even for opportunistic infections, SP chromosomes may mediate pathogen adaptation to human body conditions, such as higher temperatures and alkaline pH and iron-poor environments. Given these findings, we hypothesize that certain adaptive genetic traits are important for the establishment of Fusarium keratitis and in the compartmentalized F. oxysporum genome, these genetic traits are likely to present in the SP chromosomes. Capitalizes on our understanding of SP chromosomes that contribute directly to fungal pathogenicity, this R01 project will identify pathogenic SP chromosomes, and establish high throughput screening pipeline to identify virulence factors using transcriptomics, forward/reverse genetics and experimental evolution approaches. The achieved aims will enhance our understanding molecular mechanisms underlying fusarium keratitis, which can be used to develop novel antifungal therapies.